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Abstract:

A power factor correction converter includes an output voltage error
amplifier which functions as a proportioning device in a low-frequency
range in order to stabilize the output voltage by feedback control and
obtains a reference current amplitude value vm by multiplying an error ev
between a desired output voltage value Vref and a detected output voltage
value vo by a predetermined proportionality factor. A factor element
multiplies the reference current amplitude value by a predetermined
factor and adds the resulting value to a reference value to obtain a
desired output voltage value. The factor element functions as a low-pass
filter by changing the desired output voltage value Vref in accordance
with the reference current amplitude value vm in a low-frequency range
and reducing the factor value in a high-frequency range.

Claims:

1. A power factor correction converter comprising: a rectifier circuit
arranged to rectify an alternating-current voltage received from an
alternating-current input power supply; a series circuit connected to a
trailing portion of the rectifier circuit and an inductor and a switching
element; a rectifying and smoothing circuit connected in parallel with
the switching element; a switching control circuit arranged to on/off
controls the switching element so that input current received from the
alternating-current input power supply has a shape similar to a shape of
the alternating-current voltage; an input voltage detection circuit
arranged to detect an input voltage received from the alternating-current
input power supply; an inductor current detection circuit arranged to
detect current passing through the inductor; and an output voltage
detection circuit arranged to detect an output voltage of the rectifying
and smoothing circuit; wherein the switching control circuit defines, as
a reference current amplitude value, a product of an output voltage
error, the output voltage error being an error between a desired output
voltage value and a value of the detected output voltage, and a value of
the detected input voltage and controls the on-time of the switching
element in accordance with a difference between the reference current
amplitude value and current passing through the inductor; and the
switching control circuit includes an output voltage control value
correction circuit arranged to correct one of the desired output voltage
value and the output voltage error using a value proportional to the
reference current amplitude value.

2. The power factor correction converter according to claim 1, wherein
the switching control circuit and the output voltage control value
correction circuit include a digital signal processor arranged to
maintain a digital value corresponding to the desired output voltage
value; and the output voltage control value correction circuit is
arranged to correct the digital value using the value proportional to the
reference current amplitude value.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an AC-DC converter that receives
an alternating-current power supply and outputs a direct-current voltage
and, in particular, to a PFC (power factor correction) converter that
suppresses harmonic current.

[0003] 2. Description of the Related Art

[0004] Electric apparatuses connected to a commercial power supply are
subjected to harmonic current restriction corresponding to their power
capacity. Switching power supply devices that receive a commercial power
supply typically include a PFC converter in order to satisfy such a
restriction.

[0005] A general switching power supply device using a commercial
alternating-current power supply as an input power supply rectifies and
smoothes the commercial alternating-current power supply to convert it
into a direct-current voltage and then switches the direct-current
voltage in a DC-DC converter. Thus, the input current is discontinuous
and significantly deviates from a sine wave. This results in harmonic
current.

[0006] For this reason, a PFC converter is disposed between a full-wave
rectifier circuit and a smoothing circuit including a smoothing capacitor
in order to suppress the harmonic current.

[0007] This PFC converter includes a chopping circuit and operates so that
the input current waveform has a sinusoidal shape similar to and in phase
with the input voltage waveform. Thus, harmonic current is suppressed to
a certain level or below, and the power factor is improved.

[0008] Generally known control theories include P (proportional) control,
PI (proportional-integral) control, and PID
(proportional-integral-differential) control. PFC converters generally
use P control, since responsiveness is more important than the
steady-state characteristics of the output voltage.

[0009] Examples of PFC converters that perform P control include Japanese
Unexamined Patent Application Publication No. 07-87744. FIG. 1 is a
circuit diagram of a PFC converter described in Japanese Unexamined
Patent Application Publication No. 07-87744. Referring to FIG. 1, the PFC
converter of Japanese Unexamined Patent Application Publication No.
07-87744 will be described.

[0010] In FIG. 1, a step-up voltage converter is provided. This converter
obtains a voltage vr by rectifying an alternating-current voltage va of a
commercial power supply using a rectifier circuit 1, provides the voltage
vr to a reactor 2, interrupts current passing through the reactor 2 using
a switching transistor 3, and extracts a voltage generated at the reactor
2 during the current interruption via a diode 4 as an output voltage vo,
as well as smoothes and stabilizes the extracted voltage using a
capacitor 5.

[0011] A value vo detected by a voltage divider 6, of the output voltage
vo is provided to an error amplification circuit 7, and an error voltage
ve indicating the difference between the detected value vo and a set
value vs therefor is output. A multiplication circuit 8 receives the
error voltage ve and the rectified voltage vr, multiplies both voltages,
and outputs a voltage error signal Se, which is proportional to the error
voltage ve and has the same pulsing waveform as that of the rectified
voltage vr.

[0012] Current passing during the on-time of the switching transistor 3
and the waveform thereof are detected by a detection resistor 9, and this
current waveform signal, Sc, and the above-mentioned voltage error signal
Se are provided to a current error detection circuit 10 so that a current
error signal S1 representing the waveform difference between both signals
is output to the non-inverted input of a comparator 20. The comparator 20
compares the current error signal S1 with a sawtooth-shaped wave period
signal so, which is received from a high-frequency oscillation circuit 21
and specifies the period during which the switching transistor 3
interrupts the current, and outputs an on/off instruction signal Sw,
which is a PWM signal, to the switching transistor 3. Thus, the current
passing through the reactor 2 is interrupted at a duty ratio specified by
this on/off instruction Sw.

[0013] The PFC converter described in Japanese Unexamined Patent
Application Publication No. 07-87744 obtains a high but finite gain in a
low-frequency range. That is, even in a stable state, an error is
present. As the output voltage error ve shown in FIG. 1 increases, the
difference between the output voltage vo and the desired voltage vs
increases, thereby reducing the output voltage.

[0014] In the PFC converter described in Japanese Unexamined Patent
Application Publication No. 2007-129849, the gain is infinite in a direct
current, such that the error can be eliminated in a stable state.
However, in a transient state, such as an abrupt change in load, it takes
time to charge or discharge the capacitor, such that the time taken until
the output voltage settles is greater than that in the P-control PFC
converter described in FIG. 1.

SUMMARY OF THE INVENTION

[0015] To overcome the problems described above, preferred embodiments of
the present invention provide a PFC converter that provides both the
responsiveness of P control and the stability of PI control and that
prevents a variation in output voltage due to a variation in input
voltage or load while preventing deterioration of transient
responsiveness.

[0016] A PFC converter according to a preferred embodiment of the present
invention preferably includes a rectifier circuit arranged to rectify an
alternating-current voltage received from an alternating-current input
power supply, a series circuit connected to a trailing portion of the
rectifier circuit and including an inductor and a switching element, a
rectifying and smoothing circuit connected in parallel with the switching
element, a switching control circuit arranged to on/off control the
switching element so that input current received from the
alternating-current input power supply has a shape similar to the shape
of the alternating-current voltage, an input voltage detection circuit
arranged to detect an input voltage received from the alternating-current
input power supply, an inductor current detection circuit arranged to
detect current passing through the inductor, and an output voltage
detection circuit arranged to detect an output voltage of the rectifying
and smoothing circuit, wherein the switching control circuit defines, as
a reference current amplitude value, the product of an output voltage
error, the output voltage error being the error between a desired output
voltage value and a detected value of the output voltage, and a detected
value of the input voltage and controls the on-time of the switching
element in accordance with the difference between the reference current
amplitude value and current passing through the inductor, and the
switching control circuit includes an output voltage control value
correction circuit arranged to correct one of the desired output voltage
value and the output voltage error using a value proportional to the
reference current amplitude value.

[0017] In the PFC converter according to a preferred embodiment of the
present invention, the switching control circuit and the output voltage
control value correction circuit preferably include a digital signal
processor arranged to hold a digital value corresponding to the desired
output voltage value and the output voltage control value correction
circuit is preferably arranged to correct the digital value using the
value proportional to the reference current amplitude value.

[0018] According to various preferred embodiments of the present
invention, a variation in output voltage due to a variation in input
value or load is effectively prevented while deterioration of transient
responsiveness is also effectively prevented.

[0019] The above and other elements, features, steps, characteristics and
advantages of the present invention will become more apparent from the
following detailed description of the preferred embodiments with
reference to the attached drawings.

[0021]FIG. 2 is a circuit diagram of a PFC converter according to a first
preferred embodiment of the present invention.

[0022] FIGS. 3A to 3C show waveform diagrams of the voltage or current of
a PFC converter in a switching period in a state in which control is
being performed in a continuous current mode.

[0023]FIG. 4 is a block diagram showing the processes performed by a
digital signal processing circuit shown in FIG. 2.

[0024] FIGS. 5A and 5B show block diagrams about feedback control of the
output voltage.

[0025]FIG. 6 is a circuit diagram of an output voltage error amplifier
according to a second preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Preferred Embodiment

[0026] A PFC converter according to a first preferred embodiment of the
present invention will be described with reference to FIGS. 2 to 6.

[0027]FIG. 2 is a circuit diagram of the PFC converter according to the
first preferred embodiment. In FIG. 2, numerals P11 and P12 are the input
ports of a PFC converter 101, and numerals P21 and P22 are the output
ports of the PFC converter 101. An alternating-current input power supply
vac, which is a commercial alternating-current power supply, is input
into the input port P11 and P12, and a load circuit 100 is connected to
the output ports P21 and P22.

[0028] The load circuit 100 is preferably, for example, a circuit
including a DC-DC converter and an electronic device that receives power
supply therefrom.

[0029] A diode bridge B1, which full-wave rectifies the
alternating-current voltage of the alternating-current input power supply
vac, is disposed in the input stage of the PFC converter 101. The diode
bridge B1 corresponds to a "rectifier circuit" in preferred embodiments
of the present invention. A series circuit preferably including an
inductor L1, a switching element Q1, and a current detection resistor
Rcd, is connected to an output of the diode bridge B1. A rectifying and
smoothing circuit preferably including a diode D1 and a smoothing
capacitor C1 is connected in parallel with both end portions of the
switching element Q1. The inductor L1, the switching element Q1, the
diode D1, and the smoothing capacitor C1 define a step-up chopper
circuit. The current detection resistor Rcd and an input portion of a
digital signal processing circuit 13, which receives signals from the
current detection resistor Rcd, correspond to "an inductor current
detection circuit" in preferred embodiments of the present invention.

[0030] An input voltage detection circuit 11 is disposed between both
output terminals of the diode bridge B1. An output voltage detection
circuit 12 is disposed between the output ports P21 and P22. The digital
signal processing circuit 13 is preferably includes a DSP and controls
the PFC converter 101 by digital signal processing. Specifically, the
digital signal processing circuit 13 receives an output signal of the
input voltage detection circuit 11 so as to detect the voltage phase of
the alternating-current input power supply. The digital signal processing
circuit 13 also receives an output signal of the output voltage detection
circuit 12 so as to detect the output voltage. The digital signal
processing circuit 13 also turns on or off the switching element Q1 at a
predetermined switching frequency.

[0032] The digital signal processing circuit 13 also preferably includes
ports through which it communicates with the load circuit 100, and, for
example, communicates data or receives or outputs signals, always
transmits the converter state to the load circuit (electronic device),
transmits the input voltage, the output voltage, the output current
thereto, and receives the load state therefrom to incorporate it into
switching control.

[0033] FIGS. 3A to 3C are waveform diagrams of the voltage or current of
the PFC converter 101 in a switching period in a state in which control
is being performed in continuous current mode. The digital signal
processing circuit 13 performs switching control so that the average
value of current input into the PFC converter 101, that is, the average
value of current passing through the inductor L1 has a shape similar to
the full-wave rectified waveform. The passage of the input current having
a shape similar to that of the input voltage in this manner effectively
prevents harmonics and improves the power factor.

[0034] FIG. 3A is a current waveform of the average value Ii of the
current passing through the inductor L1 in a semi-period of the
commercial power supply frequency; FIG. 3B is a waveform diagram of the
current IL passing through the inductor L1 in a switching period where a
portion of the time axis is expanded; and FIG. 3c is a waveform diagram
of a drain-source voltage vds of the switching element Q1.

[0035] During the on-period Ton of the switching element Q1, the current
IL passes through the inductor L1 and rises at an inclination determined
by the voltage between both end portions of the inductor L1 and the
inductance of the inductor L1. Subsequently, during the off-period Toff
of the switching element Q1, the current IL falls at an inclination
determined by the voltage between both end portions of the inductor L1
and the inductance of the inductor L1. As shown in FIG. 3B, the current
IL passing through the inductor L1 varies in the switching period by the
width of current ripple ΔIL.

[0036]FIG. 4 is a block diagram showing the processes performed by the
digital signal processing circuit 13 shown in FIG. 2.

[0037] In FIG. 4, an addition element 31 obtains an error ev between a
desired output voltage value Vref which will be discussed later and a
detected output voltage value vo. An output voltage error amplifier 32
obtains a reference current amplitude value vm by multiplying the error
ev by a predetermined proportionality factor (generally, an error
amplifier in a PFC converter has a high-range interruption
characteristic, since the output voltage needs to be prevented from
responding to the ripple of the input voltage). A multiplier 33 obtains a
reference current value ir by multiplying the reference current amplitude
value vm by a detected input voltage value vi. An addition element 34
obtains an input current error value ei, which is the difference between
the reference current value ir and a detected inductor current value iL.
An input current error amplifier 35 generates a modulation signal D to be
provided to a pulse generator by multiplying the input current error
value ei by a predetermined proportionality factor. A pulse generator 36
outputs a pulse signal that is a binary logic signal, based on the
modulation signal D. This pulse signal is a switching control signal to
be provided to the switching element Q1. That is, the pulse generator 36
PWM modulates the switching control signal using a value proportional to
the input current error value ei. Thus, the on-time of the switching
element Q1 is controlled.

[0038] A factor element 38 generates a value by multiplying the reference
current amplitude value vm by a predetermined factor. An addition element
39 obtains the desired output voltage value Vref by adding the value
generated by the factor element 38 to a reference value vr0. The factor
element 38 and the addition element 39 correspond to "an output voltage
control value correction circuit" in preferred embodiments of the present
invention.

[0039] The factor element 38 changes the desired output voltage value Vref
in accordance with an output vm of the output voltage error amplifier 32.
For this reason, abnormal oscillation may occur depending on the
condition. In such a case, a high-range interruption characteristic is
provided to the factor element 38. Thus, even when the reference current
amplitude value vm abruptly varies, the Vref varies slowly, which
prevents a transient response.

[0040] FIGS. 5A and 5B are block diagrams about feedback control of the
output voltage. FIG. 5A is a block diagram of a feedback system
preferably including the addition element 31, the output voltage error
amplifier 32, the factor element 38, and the addition element 39 shown in
FIG. 4. FIG. 5B is a comparative example and is a block diagram in which
the factor element 38 or addition element 39 shown in FIG. 4 is not
provided.

[0041] In a feedback system according to the comparative example shown in
FIG. 5B, the error ev is obtained between the detected output voltage
value vo and the desired output voltage value Vref, the output voltage
error amplifier 32 outputs the reference current amplitude value vm, and
a controlling object (PFC converter) 50 controls the output voltage
(detected output voltage value vo) based on the reference current
amplitude value vm.

[0042] On the other hand, in the feedback system shown in FIG. 5A,
additionally, the factor element 38 preferably adds to the reference
(fixed) desired value vr0 a value obtained by multiplying the reference
current amplitude value vm by a factor so as to correct the desired
output voltage value Vref.

[0043] Changing the desired value vr0 in accordance with the reference
current amplitude value vm enables performing control so that the
difference (the difference between the detected output voltage value vo
and the desired output voltage value vre in a steady state) does not
occur while substantially performing P control.

[0044] As described above, since the digital signal processing circuit 13
is preferably defined by a DSP, the influence of signal deterioration,
noise intrusion, or element variations is eliminated, which enables
highly accurate correction of the desired value. Further, conditional
determination or conditional branching can be performed in a precise and
complicated manner. For example, when the load is relatively large, the
desired value is also relatively large, and, in this state, if it is
detected that the load has abruptly decreased, the desired output voltage
value Vref is reset to the initial value. Thus, a jump in output voltage
when the load abruptly decreases is prevented.

Second Preferred Embodiment

[0045] In the first preferred embodiment, as shown in FIGS. 2 and 4,
switching control is preferably performed using the digital signal
processing circuit 13 defined by DSP. On the other hand, a second
preferred embodiment of the present invention is an example in which the
output voltage error amplifier 32 shown in FIG. 4 is preferably defined
by an analog element.

[0046]FIG. 6 is a circuit diagram of an output voltage error amplifier
according to the second preferred embodiment. An input voltage Vref of a
non-inverting input terminal (+) of an operational amplifier OP is
represented by Formula (1) below. In Formula (1), Vm is the output
voltage of the operational amplifier OP (the output of the output voltage
error amplifier), vo is a detected output voltage value, and Vref is a
desired output voltage value.

Vref=(vr0/Rr1+vm/Rr3)/(1/Rr1+1/Rr2+1/Rr3) (1)

[0047] Note that since a capacitor Cref is connected in parallel with a
resistor Rr2, the temporal variation in the desired output voltage value
Vref decreases as the capacitance of the capacitor Cref increases. That
is, the function of a low-pass filter is provided.

[0048] As described above with respect to various preferred embodiments of
the present invention, when performing P control using a proportioning
device as an error amplifier, a difference occurs between the desired
output voltage value Vref and the output voltage vo in a steady state.
Accordingly, the desired output voltage value Vref is changed in
accordance with the difference. Since the vm and the difference are
proportional to each other, correcting the vref using a value
proportional to the vm effectively enables control of the output voltage
to a given value. If an abrupt change in the Vref destabilizes the
system, the low-pass filter characteristic is provided to change the Vref
slowly.

[0049] As a result, it is possible to make the output voltage independent
of the input voltage or load and constant while preventing deterioration
of transient responsiveness.

[0050] While preferred embodiments of the present invention have been
described above, it is to be understood that variations and modifications
will be apparent to those skilled in the art without departing from the
scope and spirit of the present invention. The scope of the present
invention, therefore, is to be determined solely by the following claims.

Patent applications by Yoshiyuki Uno, Nagaokakyo-Shi JP

Patent applications by MURATA MANUFACTURING CO., LTD.

Patent applications in class With condition responsive means to control the output voltage or current

Patent applications in all subclasses With condition responsive means to control the output voltage or current